In many known telephony devices, an amplifier whose function is to amplify the transmit signal in order to compensate for the losses which will be caused by the transport of said signal through the telephone line, receives the information signal coming from the interface module directly. The gain of the amplifier is then proportional to the mean value of the line current. However, the attenuation of the signal caused by the telephone line is not linear in relation to the length of said line and thus in relation to the mean value of the line current. It is known to be of the order of 1.2 dB/km and may be expressed in the form: EQU A(V/V)=K1.exp(-((K2/Iin)-K3)),
where A(V/V) is the attenuation of the signal, K1 is a multiplying constant, K2 and K3 are constants whose values are intrinsic to the line and are respectively of the order of 0.033 and 0.497, and Iin is the mean value of the line current. A linear compensation by means of an amplification whose gain is proportional to the mean value of the line current is thus not perfect and gives rise to variations of the sound level depending on the length of the telephone line.
It is an object of the present invention to remedy this drawback by proposing a telephony device in which the equation which defines the value of the gain of the amplifier is the reverse to that which defines the attenuation of the signal brought about by the line.